Imaging device

ABSTRACT

The present invention is an image pickup device provided with a CMOS camera which is provided with a telecentric lens to photograph a sample put in a levitation state at the center inside an electrostatic levitation furnace, a metal halide light source which is positioned on the opposite side of the sample from the CMOS camera to irradiate light with a wavelength of 400 to 450 nm toward the sample, and a digital signal processor which performs image processing for enhancing an edge of an image captured by the CMOS camera in real time to output a position of center of gravity of the sample put in the levitation state, where a blue filter is attached to the CMOS camera. Even if the sample becomes incandescent due to a high temperature, contrast of the sample against a background can be obtained by the image pickup device. In addition, position information required for levitation control of a sample with a complicated shape is outputted by the image pickup device so that an instant at which the sample with a complicated shape changes to a spherical shape one can be specified visually.

TECHNICAL FIELD

The present invention relates to an image pickup device which is used todetermine an instant at which a sample is melted while recognizing aposition of the sample put in a levitation state when performing heatingprocess on the sample in an electrostatic levitation furnace.

BACKGROUND ART

The electrostatic levitation furnace, after charging a sample inputtedbetween main electrodes utilizing electrode contact, ultraviolet rayirradiation, or heating, puts the sample to a levitation state by anelectrostatic field generated between the main electrodes, whilemaintaining the sample at a predetermined position by controlling apotential between the main electrodes or auxiliary electrodes, andirradiates laser light on the sample to heat and melt the same. Bycooling and solidifying the sample thus heated and melted, crystals canbe produced in a state that external interference has been excluded.

It is necessary to control levitation of a sample so as to preventswinging of the sample or suppress the same as much as possible throughgenerating crystal in the electrostatic levitation furnace in order toimprove quality, and it is important to recognize a position of thesample accurately in order to perform control on such sample levitation.

Conventionally, as a means of recognizing a position of a sample, forexample, there are a position recognizing method which uses laser lightas background light and detects the highest luminescent spot or astatistical center of the luminescent spots except for a portionshielded by a sample formed in an almost spherical shape using a photosensor to output position information, and a position recognizing methodwhich uses laser light as background light like the above approach andprocesses an image of a sample photographed by a CCD camera to calculatea position of the center of gravity and output the same as positioninformation.

In the conventional art, however, since a position of the center ofgravity of the sample is not calculated in the former positionrecognizing method, the method does not excel at accuracy in positionrecognition of a sample except a spherical one. As a result, there issuch a problem that it becomes considerably difficult or impossible toperform levitation control on a simple.

On the other hand, in the latter position recognizing method, theposition of the center of gravity of a sample is calculated, but sinceit takes much time to perform image processing and a sampling speedrequired for levitation control can not be secured, there is such aproblem that the latter method can be used only rarely.

Further, in case that a halogen lamp is used for the background light,when the sample becomes incandescent due to a high temperature, it isimpossible to obtain a contrast of a sample against a background, sothat laser light is adopted as the background light in the latterposition recognizing method (see FIG. 3). However, for convenience ofusing a CCD camera, there is a problem about interference of laser lightdue to a camera lens.

Moreover, in the position recognizing methods, since such a constitutionis employed that an instant at which a sample has melted is determinedby measuring a temperature of the sample using a radiation thermometer,it is always required to correct an emissivity. There is such a problemthat it is difficult to specify a melting time correctly. It is theconventional subject to solve these problems.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the subject in theconventional art, and an object of the present invention is to providean image pickup device which can obtain a contrast of a sample against abackground even if the sample becomes incandescent due to a hightemperature, and can output position information required for levitationcontrol on not only a spherical sample but also a sample with a furthercomplicated shape in real time, thereby being capable of specifying aninstant at which a sample with a complicated shape changes to aspherical one visually, that is, determining an instant at which thesample melts visually.

As the result of repeating keen examination for accomplishing the aboveobject, the present inventors have found that the above object can beaccomplished by combining a CMOS camera or a CCD camera forphotographing a sample which is provided with a telecentric lens, abackground light source which irradiates light with a wavelength of 400to 600 nm on a sample, and a digital signal processor which performsimage processing for edge enhancement in real time, and therefore havecompleted the present invention.

That is, an image pickup device according to the present invention is animage pickup device which monitors a sample to be subjected to heatingprocess in a levitation state within an electrostatic levitation furnaceto output position information, comprising: a CMOS camera or a CCDcamera for photographing a sample which is provided with a telecentriclens, a background light source which is positioned on the opposite sideof the sample from the CMOS camera or the CCD camera to irradiate lightwith a wavelength of 400 to 600 nm on the sample, and a digital signalprocessor which performs image processing for edge enhancement in realtime to output a position of center of gravity of the sample put in thelevitation state.

In a preferable embodiment of the image pickup device of the presentinvention, a metal halide light source which irradiates light with awavelength of 400 to 450 nm is used as the background light source, andin a more preferable embodiment of the image pickup device of thepresent invention, a color filter for changing spectral characteristicsis attached to the telecentric lens of the CMOS camera or the CCDcamera.

When a sample subjected to heating process within an electrostaticlevitation furnace is monitored using the image pickup device of thepresent invention, it is desirable that respective CMOS cameras or CCDcameras of two image pickup devices are arranged to be orthogonal toeach other to photograph. Further, in order to emphasize contrast of asample against a background, it is desirable that a lens for condensinglight irradiated from the background light source on a sample isprovided between the background light source and the sample, but thepresent invention is not considered limited to this constitution.

In the image pickup device of the present invention, in case that asample is subjected to heating process by the electrostatic levitationfurnace, light is irradiated from the background light source on asample put in a levitation state, contrast of the sample against abackground levitated is thereby captured by the CMOS camera or the CCDcamera, and a position of center of gravity is calculated from thecaptured image so that position information is outputted.

At that time, since the CMOS camera or the CCD camera photographing thesample is provided with the telecentric lens, a dimensional error of theimage due to magnification change of the image can be corrected, thatis, a size of the sample and a relative distance of a reference on thesample is not changed, even if the sample moves slightly on an opticalaxis, so that correct position information can be obtained.

Furthermore, since light with a wavelength of 400 to 600 nm isirradiated from the background light source, even if the sample becomesincandescent due to a high temperature, contrast of the sample against abackground is eventually obtained. In addition, as regards a capturedimage of a sample, since the digital signal processor performs imageprocessing for enhancing an edge of the image in real time to output aposition of center of gravity required for levitation control,levitation melting of the sample with a complicated shape is madepossible, so that an instant at which the sample with a complicatedshape put in the levitation state changes to a spherical shape one canbe determined visually.

In the image pickup device according to a preferable embodiment of thepresent invention, since the constitution described above is adopted,interference of light between lenses of the CMOS camera or the CCDcamera can be avoided so that the captured image is further sharpened.In the image pickup device according to a more preferable embodiment ofthe present invention, since the constitution described above isadopted, contrast of a sample against a background can be obtainedfurther surely.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic explanatory diagram showing one embodiment of animage pickup device of the present invention;

FIG. 2 is a graph showing spectral distribution characteristics of ametal halide serving as a background light source used in the imagepickup device shown in FIG. 1; and

FIG. 3 is a graph showing spectral distribution characteristics of ahalogen lamp.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be explained below in detail according to anembodiment, but a detailed constitution of the present invention is notconsidered limited to only the following embodiment.

As schematically shown in FIG. 1, an electrostatic levitation furnace 10is interiorly formed of an approximate cylindrical space, and the centerof the space is set as a levitation position for a sample A. Theelectrostatic levitation furnace 10 is provided on a peripheral wallthereof with a plural of ports for access (not shown), and openingportions 11 are provided so as to correspond to arrangement of the portsfor access.

An image pickup device 1 which monitors the sample A to be subjected toheating process in its levitation state within the electrostaticlevitation furnace 10 to output position information of the sample isprovided with a CMOS camera 2 which is mounted at the port for access inthe vicinity of the opening portion 11 to photograph the sample A put ina levitation state at the center of the interior of the electrostaticlevitation furnace 10, a metal halide light source 3 which is mounted onthe ports for access positioned on the opposite side of the sample Afrom the CMOS camera 2 to irradiate light with a wavelength of 400 to450 nm (see FIG. 2) toward the sample A and which serves as a backgroundlight sources, and a digital signal processor (DSP) 4 which performsimage processing for enhancing an edge of an image captured by the CMOScamera 2 in real time to output a position of center of gravity of thesample A put in the levitation state.

The CMOS camera 2 is provided with a telecentric lens 5, which attachesa blue filter (a color filter) 6 for changing spectral characteristics.On the other hand, a lens 7 for condensing which condenses lightirradiated from the metal halide light source 3 on the sample A isprovided between the metal halide light source 3 and the opening portion11.

In this embodiment, two sets of the image pickup devices 1 are prepared,and both the devices 1, 1 are arranged such that an optical axis L1connecting the CMOS camera 2 and the metal halide light source 3 of oneof the image pickup devices 1 and an optical axis L2 connecting the CMOScamera 2 and the metal halide light source 3 of the other of the imagepickup devices 1 are orthogonal to each other.

In case that a sample A is subjected to heating process by theelectrostatic levitation furnace 10, lights from the respective metalhalide light sources 3, 3 of the image pickup devices 1, 1 arealternately irradiated on the sample A put in a levitation state,contrasts of the sample A against backgrounds emerging due to theirradiation are captured by the CMOS cameras 2, 2, and a position ofcenter of gravity of the sample is calculated from these images to beoutputted as position information.

At that time, since the CMOS camera 2 photographing a sample is providedwith the telecentric lens 5, even if the sample A moves slightly on theoptical axis L1 (or on the optical axis L2), a size of the sample A donot change, so that accurate position information can be obtained.

Besides, since light with a wavelength of 400 to 450 nm is irradiatedfrom the metal halide light source 3 serving as a background lightsource, even if the sample A becomes incandescent due to a hightemperature (2500K or so), contrast of the sample against a backgroundcan be obtained. In addition, as regards the captured image of thesample A, since the digital signal processor 4 performs image processingfor enhancing an edge of the image at sampling intervals of 0.5 to 1msec (desirably, or less) to output a position of center of gravity of asample required for levitation control, levitation melting of a sample Awith a complicated shape is made possible, so that an instant at whichthe sample with a complicated shape put in a levitation state changes toa spherical shape can be determined visually.

Further, in the image pickup device 1, since the metal halide lightsource 3 is adopted as the background light source, interference oflight can be prevented from occurring between the lenses of the CMOScameras 2, so that the captured image is further sharpened. Moreover, inthe a image pickup device 1, since the blue filter (the color filter) 5which changes spectral characteristics is attached to the CMOS camera 2and the lens for condensing 7 is provided between the metal halide lightsource 3 and the opening portion 11, contrast of the sample A against abackground is obtained further securely.

INDUSTRIAL APPLICABILITY

As explained above, in the image pickup device of the present invention,since the constitution is adopted, when a sample is subjected to heatingprocess by an electrostatic levitation furnace, even if the samplebecomes incandescent due to a high temperature, contrast of the sampleagainst a background can be obtained and a position of center of gravityrequired for levitation control can be accurately outputted at a highspeed. As a result, such a very high advantage can be attained that aninstant at which a sample with a complicated shape put in a levitationstate changes to a spherical shape one can be determined visually.

Further, in the preferable embodiment of the image pickup device of thepresent invention, since the constitution is adopted, a captured imageobtained by a CMOS camera or a CCD camera can be more sharpened.Additionally, since the image pickup device as the more preferableembodiment of the present invention is constituted in the above manner,contrast of a sample against a background can be obtained furthersecurely.

1. An image pickup device which monitors a sample to be subjected toheating process put in a levitation state within an electrostaticlevitation furnace to output position information, comprising: a CMOScamera or a CCD camera for photographing a sample which is provided witha telecentric lens, a background light source which is positioned on theopposite side of the sample from the CMOS camera or a the CCD camera toirradiate light with wavelength of 400 to 60 nm on the sample, and adigital signal processor which performs image processing for edgeenhancement in real time to output a position of center of gravity ofthe sample put in the levitation state.
 2. An image pickup deviceaccording to claim 1, wherein a metal halide light source whichirradiates light with a wavelength of 400 to 450 nm is used as thebackground light source.
 3. An image pickup device according to claim 1,wherein a color filter which changes spectral characteristics isattached to the telecentric lens of the CMOS camera or the CCD camera.